Portion of a humidifier tub



FIG. 1 is a perspective view of portion of a humidifier tub according toour design;

FIG. 2 is a front view thereof;

FIG. 3 is a top view thereof; and,

FIG. 4 is a right side view thereof with the left side view thereofbeing a mirror image thereof.

Where included, broken lines showing environment or structure are forillustrative purposes only and form no part of the claimed design.

The ornamental design for portion of a humidifier tub, as shown anddescribed.